This invention relates generally to the field of sonar, and more particularly to sonar apparatus or systems carried by a moving platform, such as a ship or a weapon, and having the capability of automatically tracking one or more objects or "targets" of interest.
Torpedoes or other weapons have been contemplated as carrying an active sonar that operates to acquire and track a vessel or other target of interest for the purpose of guiding the torpedo autonomously to that target. Sonar is also used in defensive systems carried by vessels likely to become targets of interest to detect the presence of and to track the progress of attacking weapon systems. Either the offensive or the defensive system may transmit a variety of countermeasure signals or deploy decoys which operate either actively or passively in an effort to cause the sonar of the other to lock on or track the decoy rather than the torpedo or the vessel and thereby thwart the offensive or defensive purposes thereof. Accordingly, it is desirable that a target tracking sonar, either as part of an offensive weapon such as a torpedo or as part of a defensive system, have the return signal post-processing, discriminatory editing capability of distinguishing between a real sonar target of interest and other objects, either deployed or natural, such as decoys, schools of fish, whales, or the like, and to rapidly and automatically act on such distinguishing ability to reject targets not of interest. It is well known that at long range, one means of discriminating real targets from counter measures is to look for inconsistancies between measurements of apparent range and range rate when using active sonar to develop track data. Present weapon post-processing editors either do not attempt to discriminate by track data, or do so in a crude manner using raw data and looking merely for consistency of position and Doppler.
Tracking of a moving object using a Kalman filter based approach has been extended from radar to sonar application by developing the combination of an acceleration input vector estimator, a detector for sensing target maneuvers, and a simple Kalman filter updated only when the estimated input vector exceeds or threshold. That development is discussed at length in an article entitled "A Kalman Filter Based Tracking Scheme With Input Estimation" published in IEEE Transactions, Aerospace and Electronic Systems. AEA-15, No. 2, March 1979.